Human Insulin is a polypeptide hormone involved in regulation of glucose in blood and body fluids. Production deficiency leads to type 1 or type 2 diabetes. Type 1 is especially Insulin dependent diabetes. Earlier, Insulin used to be supplemented from animal sources (bovine and pig), which often results in undesirable allergic immune response or hypersensitive reaction on continual administration for longer periods. The next generation of Humanized Insulin was produced in E. coli by recombinant DNA technology and is being successfully used for the past several years. Although recombinant human Insulin is being expressed in different hosts through patented processes to meet the diabetes therapeutic requirements, the demand is growing and forcing the man kind to explore new and modified methods to produce commercially viable quantities.
Recombinant human Insulin currently available in the market is produced from at least three different expression systems i.e. E. coli, Pichia pastoris and Hansenula polymorpha. Over expression in E. coli results in proteins accumulating as insoluble inclusion bodies. Solubilization and refolding of the recombinant Insulin from the inclusion bodies requires use of chaotropic chemicals such as guanidine hydrochloride, urea, etc. and presence of traces of these chemicals in the final product even after extensive purification could be hazardous. Alternatively, proteins can be expressed in yeast system and secreted out into the medium at much higher levels in soluble form. However, levels of expression obtained in each yeast system differed from protein to protein for unknown reasons.
The two chains of Human Insulin are also being expressed separately using two different vectors and assembled together in-vitro after purification. Disulphide linkages between two chains is facilitated by chemical methods